Check the picture attached.
let m(VTI)= m(ITU)=a and let m(VUI)= m(IUT)=b
Then, in triangle TUV:
2a+2b+c=180°
2(a+b)+c=180°
c=180°-2(a+b)
In triangle TUI:
a+b+109°=180°
a+b=180°-109°=71°
substitute in c=180°-2(a+b):
c=180°-2(a+b)=180°-2*71°=180°-142°=38°
let m(VTI)= m(ITU)=a and let m(VUI)= m(IUT)=b
Then, in triangle TUV:
2a+2b+c=180°
2(a+b)+c=180°
c=180°-2(a+b)
In triangle TUI:
a+b+109°=180°
a+b=180°-109°=71°
substitute in c=180°-2(a+b):
c=180°-2(a+b)=180°-2*71°=180°-142°=38°